The present invention relates to valves of the type having a pivoted throttle plate or butterfly member and particularly valves of this type which are employed for valving flow from a single inlet to a single outlet or for diverting flow from one of a plurality of outlets to another outlet. Butterfly valves are often employed where the force available to actuate the valve is minimal and thus the fluid pressure forces acting on the valving member must be maintained at a relatively low level. Diverter valves of this type are often employed in automotive applications for controlling flow of engine coolant to be either recirculated through the engine or diverted to a heat exchanger utilized for passenger compartment heating. Such automotive heater valves are typically actuated by small electric servomotors or diaphragm operated vacuum actuators which due to size and weight requirements are capable of providing only a few ounces of force for opening the valve. Butterfly-type valves have been found to be particularly suitable for such low-operating force applications because the pressure forces of the fluid act upon the throttle member or butterfly on opposite sides of the pivot and are generally balanced and thus the force required to move the butterfly is minimized.
In certain valve applications it is desired to provide a diverter valve having a plastic body such as high-volume production automotive applications where manufacturing costs must be minimized. In plastic bodied valves it is required that the butterfly member have some degree of resiliency in order to effect a seal about the periphery of the butterfly in either of the closed or first or second diverter position. It is also desired to have a resilient periphery to the butterfly member to accommodate very small foreign particles in the fluid being valved in order to prevent blocking of the butterfly member from sealing about its periphery against the wall of the valving chamber about the ports of the valve. Thus, it has been desired to provide a low cost resilient butterfly member in a valve, particularly a diverter valve of the type employed in automotive heater flow control systems which can seal and block flow in a desired position with a relatively low actuating operating force applied to the valve member.